Vibrating sensors, such as for example, vibrating densitometers and Coriolis flowmeters are generally known, and are used to measure mass flow and other information for materials flowing through a conduit in the flowmeter. Exemplary Coriolis flowmeters are disclosed in U.S. Pat. Nos. 4,109,524, 4,491,025, and Re. 31,450, all to J. E. Smith et al. These flowmeters have one or more conduits of a straight or curved configuration. Each conduit configuration in a Coriolis mass flowmeter, for example, has a set of natural vibration modes, which may be of simple bending, torsional, or coupled type. Each conduit can be driven to oscillate at a preferred mode.
Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter, is directed through the conduit(s), and exits the flowmeter through the outlet side of the flowmeter. The natural vibration modes of the vibrating system are defined in part by the combined mass of the conduits and the material flowing within the conduits.
As material begins to flow through the flowmeter, Coriolis forces cause each point along the conduit(s) to have a different phase. For example, the phase at the inlet end of the flowmeter lags the phase at the centralized driver position, while the phase at the outlet leads the phase at the centralized driver position. Pickoffs on the conduit(s) produce sinusoidal signals representative of the motion of the conduit(s). Signals output from the pickoffs are processed to determine the time delay between the pickoffs. The time delay between the two or more pickoffs is proportional to the mass flow rate of material flowing through the conduit(s).
Meter electronics connected to the driver generate a drive signal to operate the driver and determine a mass flow rate and other properties of a material from signals received from the pickoffs. The driver may comprise one of many well-known arrangements; however, a magnet and an opposing drive coil have received great success in the flowmeter industry. An alternating current is passed to the drive coil for vibrating the conduit(s) at a desired flow tube amplitude and frequency. It is also known in the art to provide the pickoffs as a magnet and coil arrangement very similar to the driver arrangement. However, while the driver receives a current which induces a motion, the pickoffs can use the motion provided by the driver to induce a voltage. The magnitude of the time delay measured by the pickoffs is very small; often measured in nanoseconds. Therefore, it is necessary to have the transducer output be very accurate.
A dual-tube Coriolis sensor is typically designed with symmetric features for the flow path and structural components of the sensor. This approach results in a balanced sensor through matched elastic and inertial loads. An imbalance in the Coriolis forces could occur if the tubes had unmatched flow rates, which could lead to reduced flow accuracy and susceptibility to external loads and vibrations.
The constraint of a symmetric flow path design limits sensor compactness, manufacturing approaches for the manifold, and flexibility of sensor layout to best match certain integration requirements. Since tube axis parallelism is required, dual tube sensors have not been designed with single-piece manifolds as would often be produced with metal or plastic parts by a permanent mold. The result is a significant limitation on cost reduction and potential manufacturing approaches.
Therefore, there is a need in the art for an apparatus and related method to allow asymmetric flow through a flowmeter, yet provide accurate flowmeter readings. Additionally, asymmetric manifold design allows for more compact and effective flowmeter design.
The present invention overcomes the above difficulties and other problems, and an advance in the art is achieved.